The present invention relates to a hydraulically operated device adapted to be connected in a pipe string, specifically coiled tubing. For example, the device can be used in order to facilitate pushing of the string into highly deviated or horizontal wells in connection with working, and in maintenance operations such as logging, assembling or disassembling parts, acid and sand washing etc.
It has previously been proposed to provide drill strings with hydraulically operated devices or vibrators to facilitate the advance of the string. Thus, U.S. Pat. No. 4,384,625 proposes subjecting the drill string to vibrations in the form of resonance oscillations to reduce the friction between the drill string and bore hole wall in deviated wells to extend the reach in rotary drilling. As an example of a vibrator the patent refers to a fluid operated eccentric weight, implying substantially transversal vibrations.
U.S. Pat. No. 3,235,014 describes a method and apparatus for generating axial vibrations through a drilling swivel to transmit a percussive effect to the drill bit. Furthermore, various types of hydraulic hammer or percussion tools are known, which are intended for loosening sticking drill strings. An example of this type of tool is disclosed in NO patent 171 379.
Coiled tubing has substantially lower mass and diameter than drill pipes, which means that a transversally acting resonance vibrator with accompanying hydraulic motor as proposed in the above U.S. Pat. No. 4,384,625 would be rather ineffective when used in connection with coiled tubing. The main object of the invention, therefore, is to provide a device that effectively reduces friction, both at the coiled tubing head (lowermost tool section) as well as upwardly along the coiled tubing itself.